The function of A-kinase anchoring proteins (AKAPs) is to sequester the cAMP-dependent protein kinase (PKA) holoenzyme to specific subcellular locations. PKA is a broad-specificity signaling enzyme whose function is important for several physiological processes. In addition to PKA, AKAPs interact with numerous other signaling molecules in order to nucleate multi-protein complexes. This form of regulation contributes to the specificity of cAMP signaling by ensuring the efficient activation of PKA in close proximity to the appropriate intracellular targets. Previous studies in the Scott lab have indicated that the 220-kDa anchoring protein, termed AKAP220, assembles the protein phosphatase, PP1, with anchored PKA. More recent evidence suggests that AKAP220 can also interact with the Ser/Thr kinase, GSK-3. I propose that in response to certain stimuli, the role of anchored PKA and PP1 is to counterbalance one another in the regulation of GSK-3. The specific aims of this proposal are to 1) test whether compartmentalization of GSK- 3 with PKA and PP1 by AKAP220 reveals a novel mechanism for regulating GSK-3 in vivo and 2) examine the role of AKAP220 by testing the hypothesis that AKAP220 null mice will reveal defects in PKA signaling.